Electron discharge apparatus



M 6, 143: H. MQTZ 2,323,560

ELECTRON DISCHARGE APPARATUS Filed Dec. 11, 1940 INVENTOR. //4/v.s W072 Patented July 6, 1943 ELECTRON DISCHARGE APPARATUS HansMotz, Blackheath, London, England, assignor to International Standard Electric Corporation, New York, N. Y.

Application December 11, 1940, Serial No. 369,514

I In Great Britain July 5, 1940 Claims. (01. 250 27.51

This invention relates to electron discharge apparatus foroperation at extremely high frequencies and of the kind wherein an electron beam traverses a high frequency field and is thereby' either modulatedin'velocity or caused I that application, also the discharge devicesdisclosed in Patent No. 2,190,668 to Llewellyn.

In such electron discharge apparatus it is advantageous to use focussed electron beams of large current and current density. It has been found difficult to produce such beams because of the space charge set up by the beam. The space charge tends to decelerate the beam, and in the extreme case stops the beam completely, thus forming an unwanted virtual cathode somewhere along the intended path of the beam.

According to the present invention this difliculty is overcome by generating suitablepositive ions for the purpose of neutralising the space charge. The ions may be generated by admitting to the tube a certain amount of a suitable gas at a suitable pressure, and producing the ions by the impact of electrons. According to an alternative method specifically claimed in my co-pending application Serial No. 369,515, filed on even date herewith, a beam of positive ions is passed along the electron path in a direction opposite to the electron beam.

In particular, barium ions may be utilised because they would have three other useful effects. Firstly, any barium ions which may be neutralised and condensed on any inner surface of the tube act as a getter. Secondly, if a surface coated with a barium compound is used as an electron source, barium from the beam can be used to replenish the barium content of the electron emitting surface. Thirdly, the barium ions also tend to neutralise the space charge near the electron emitting surface and thus make it possible to use dispenser cathodes or electron emitting surfaces of complex shape, such as cathodes comprising vanes or tubes coated with emissive material and located within an enclosing metal cylinder open at one end.

Caesium ions are also suitable for reasons similar to the ones stated above. Caesium ions have an advantage in that the caesium after use in its ionised state may be recovered by bringing different parts of the tube to such temperatures,

that caesium is evaporated from these surfaces which are kept warm, and condensed in aspecially arranged cooled region.

Mercury may alternatively be employed. In this case a drop of mercury is introduced into the evacuated container and the operating conditions are arranged such that the pressure of the order of 10- to 10- mm. mercury is obtained.

The electron beam may be made to heat the ion source; conversely the ion beam may be used to heat the electron source; the amount of heating current for the ion or electron sources can then be reduced once the tube is running.

The ion beam may be produced by various methods. In one method those substances are used which, when heated, generate a vapour which can be ionised by the hot wire method. In particular the vapour can be made to pass a hot wire mesh and the ions formed can be focussed by the usual electric and magnetic lenses.

An electron discharge device of the klystron oscillator type modified in accordance with the invention is shown diagrammatically in the single figure of the accompanying drawing.

R and RI are the toroidal resonators of the klystron with central grids or apertures G and back-coupling LI. The resonator are joined by drift tube T. Electrons from a cathode K are concentrated in a beam by focussing electrodes represented by FE. In passing through the resonator RI, (that is, across the first gap in the resonator system) they are modulated in velocity. They subsequently become bunched in the drift tube 'I' and are retarded in the second resonator R (that is, in traversing the second gap of the resonator system), thereby yielding energy to the resonator B. Part of the energy in resonator R is fed back over the coupling Ll to excite resonator RI.

In accordance with the present invention, an ionisable gas or vapour is introduced into the device or as shown in the figure provision is made for generating and ionising a gas or vapour during operation of the device.

In the structure shown, a barium compound such as barium barylliate or barium metal B is provided in a container C surrounded by a resistance heater H. A series of wires W forming a grid and adapted to reach a high temperature during operation (either by bombardment or by means of an external current supply source) is arranged in front of the container C for ionising barium vapourised from the container. The

wires W, in the case of barium, are composed of a material such as oxidised tungsten having a work function, when hot, which i larger than the ionisation potential of the gas to be ionised. The barium ions in the structure shown are concentrated in a beam towards the cathode by means of a focussing electrode system represented by F I The whole structure shown may be enclosed in a vacuum-tight envelope E with suitable leading-in conductor sealed in it. Alternatively the various beam-forming electrodes may be disposed at the ends of a narrow glass or like tube projecting through the resonator system. In this case simple apertures are provided in the resona tors instead of grids.

Various modifications within the scope of the appended claims will be readily appreciated.

What is claimed is:

1. An electron discharge device of the resonator type having a first resonator and a second resonator, a drift tube connected there-between, said resonators and drift tube having an electron beam path extending therethrough, a collector forelectrons at one end of said path, electron gun means at the other end of said path for projecting a beam of electrons along said path toward said collector, and an ionizable gaseous atmosphere Within said resonators and drift tube at a negative-space-charge reducing pressure.

2. An electron discharge device according to claim 1, wherein said gaseous atmosphere includes the vapor of an alkaline metal.

3. An electron discharg device according to claim 1, wherein said gaseous atmosphere includes the vapor of barium.

4. An electron discharge device according to claim 1, wherein said gaseous atmosphere includes the vapor of caesium.

5. An electron discharge device of the resonator type having a first resonator and a second resonator, a drift tube connected therebetween, said resonators and drift tube having an electron beam path extending therethrough, a collector for electrons at one end of said path, and electron gun means at the other end of said path for projecting a beam of electrons along said. path.

toward said collector, and an ionizable gaseous atmosphere within said resonators and .drift tubeincluding mercury vapor at a pressure of th or! der of l0- to 10 millimeters of mercury.

HANS MOTZs 

